1. Field of the Invention
The present invention relates to a CATV pay-channel transmission method which distributes paid-subscriber television signals to subscribers.
2. Description of the Prior Art
In conventional CATV systems using a standard coaxial cable transmission path unauthorized reception of pay-channel programming is prevented by the transmitter scrambling out-going pay-channel television signals. A signal receiver is provided to CATV subscribers to descramble the received signal using various methods, including a "key" which unlocks the scrambling format or an electrical filter which passes only the paid-for channels. Such methods have been described in "CATV in the satellite broadcasting age", p. 252, (1987), compiled by Cable Broadcasting Section, Broadcasting Administration Department, (Japanese) Ministry of Posts and Telecommunications.
However, there has always been the possibility of unauthorized reception of pay-channel programming enabled by tampering with the electrical circuits of the signal receiver. Picture deterioration in the descrambled, demodulated signal has also been a problem. On the other hand, unauthorized reception of digitally processed scrambled signals is difficult and there is no degradation of the demodulated signal, but the descrambler cost is higher due to the need for A/D and D/A converters.